The present invention relates to a tape reel assembly for a data storage tape cartridge. More particularly, it relates to a tape reel assembly including a hub sleeve and spherical piece configured to reduce tape reel wobble, and a method for manufacture thereof.
Data storage tape cartridges have been used for decades in the computer, audio and video fields. The data storage tape cartridge continues to be an extremely popular device for recording large volumes of information for subsequent retrieval and use.
A data storage tape cartridge generally consists of an outer shell or housing maintaining at least one tape reel assembly and a length of magnetic storage tape. The storage tape is wrapped about a hub portion of the tape reel assembly and is driven through a defined tape path by a driving system. The housing normally includes a separate cover and base, the combination of which forms an opening (or window) at a forward portion thereof for allowing access to the storage tape by a read/write of a tape drive. This interaction between storage tape and head may take place within the housing (for example, with a mid-tape load design), or the storage tape may be directed away from the housing to an adjacent area at which the read/write head is located (for example, with a helical drive design or a leader block design). Where the tape cartridge/drive system is designed to direct the storage tape away from the housing, the data storage tape cartridge normally includes a single tape reel assembly. Conversely, where the tape cartridge/drive system is designed to provide head/storage tape interaction within or very near the housing, a two- or dual-tape reel assembly configuration is typically employed.
With the dual-tape reel configuration, the tape path is defined by the location of the tape reels maintaining storage tape, as well as various tape guides positioned within the housing. Each tape reel is normally rotatably associated within the housing, and includes a hub and opposing flanges. The hub forms an outer, tape-winding surface about which the storage tape is wound. The flanges are disposed at opposite ends of the hub, and are spaced to approximate the height of the storage tape. Generally, the storage tape extends between the two hubs, along the tape guides. The tape guides are, in turn, strategically positioned within the housing such that at the cartridge window, the storage tape is parallel to a plane of the window.
In addition to facilitating proper positioning of the storage tape at a desired level in the area of the cartridge window, alignment of the tape reels, and in particular the respective hubs, plays a crucial role in minimizing tape wear. Tape reel xe2x80x9calignmentxe2x80x9d is normally understood to refer to spacing between the hub and the cover (or other section of the housing). If the hub or hubs are not properly spaced relative to the cover, the storage tape will not be optimally positioned along the tape guide(s). Over time, this undesirable interaction may lead to wrinkling or other forms of tape deterioration. In other words, a cross-webbed tension is generated across the storage tape, possibly causing edge wear. Even further, tape reading errors may result at the high-tension side of the storage tape. Because current data writing/reading systems make use of nearly the entire width of the storage tape and utilize increasingly smaller data tracks along the storage tape width, it is imperative that every effort be made to ensure proper hub alignment.
The conventional technique for rotatably associating the tape reel within the housing is to press fit a straight tape reel pin into one section of the housing, such as the cover. Alternatively, the tape reel pin is press fitted into a separate base plate element that is secured within the housing. Regardless, the tape reel hub is formed to include an axial bore that receives the tape reel pin. The axial bore is slightly larger in diameter then the tape reel pin so that the hub can freely rotate about the tape reel pin. Further, the axial bore terminates at an internal, axial thrust surface. Upon final assembly, a leading end of the tape reel pin contacts or abuts the thrust surface. During use, the tape reel assembly is engaged by a tape drive mechanism and directed axially against the tape reel pin. Subsequently, the tape drive mechanism rotates the tape reel assembly about the stationary tape reel pin, with the thrust surface bearing the axial load placed upon the tape reel assembly. Notably, the hub is typically a molded plastic article, whereas the tape reel pin is stainless steel or other metal. The loaded, rotational contact between the thrust surface and the leading end of the tape reel pin can result in wear of the plastic hub. Over time, this wear can result in hub misalignment.
To overcome the above-described wearing issues presented by plastic hub/metal tape reel pin interaction, a recent tape reel assembly design modification includes a metal ball disposed between the axial thrust surface and the tape reel pin. For example, as described in U.S. Pat. No. 6,040,966, a stainless steel ball is placed within the hub bore to bear the axial load of the tape reel assembly relative to the pin. Effectively, the stainless steel ball rotates against the leading end of the tape reel pin, thereby minimizing hub wear. While this approach is highly effective in eliminating wear concerns, as well as efficiently compensating for variations in tape reel pin height, one potential issue has been identified. In particular, the hub, and thus the tape reel assembly, may xe2x80x9cwobblexe2x80x9d (e.g., deflect or otherwise deviate from axial alignment with the tape reel pin) slightly at the hub/ball interface. Normally, the degree of wobble is insignificant. However, with increased levels of wobble and/or more stringent operating parameters such as reduced-size data tracks, the hub wobble may lead to servo-tracking errors, tape wear, etc.
Data storage tape cartridges are important tools used to maintain vast amounts of information. With increasingly complex writing/reading and magnetic tape technology, design of the data storage tape cartridge must evolve to provide extremely accurate, consistent tape positioning. To this end, any potential error sources should be addressed. Therefore, a need exists for a tape reel assembly configured to reduce hub wobble and wear.
One aspect of the present invention relates to a data storage tape cartridge that includes a housing, a tape reel pin, a tape reel assembly, and a storage tape. The housing includes a first housing section and a second housing section. The tape reel pin extends in a generally perpendicular fashion relative to an interior surface of the first housing section. With this configuration, the tape reel pin provides a cylindrical side surface and terminates in a leading end. The tape reel assembly is rotatably associated with the tape reel pin and includes a hub, a spherical piece and a sleeve. The hub defines an axial bore. The spherical piece is secured to the hub and provides a thrust surface for contacting the leading end of the tape reel pin. The sleeve is likewise disposed within the axial bore and defines a journal bearing surface corresponding with the cylindrical side surface of the tape reel pin. Finally, the storage tape is maintained by the hub. In one preferred embodiment, the spherical piece and the sleeve are insert molded into the tub. With this one preferred configuration, the spherical piece and the sleeve a precisely centered relative to an outer, tape receiving surface of the hub. In another preferred embodiment, the sleeve is a drawn bronze material. By controlling a bore tolerance of the sleeve, the opportunity for, and degree of, hub wobble is greatly reduced.
Another aspect of the present invention relates to a method of manufacturing a tape reel assembly for use with the data storage tape cartridge including a tape reel pin. The method includes providing a hub die cavity comprising a mold shell and a core pin. The mold shell is configured to produce a hub having an outer cylindrical surface for maintaining a storage tape. The core pin, in turn, terminates in a leading end. With this in mind, the mold shell is removably postionable about the core pin. A sleeve, defining an inner diameter approximating a diameter of the tape reel pin, is placed over the core pin. A spherical piece is placed above the leading end of the core pin. The mold shell is then placed about the core pin. Finally, plastic is injected into the mold shell to form a hub. In this regard, the sleeve and the spherical piece are insert molded into the hub and combine to define an axial bore for receiving the tape reel pin. In one preferred embodiment, an injection pressure generated during the step of injection molding forces the spherical piece into a seated relationship with the leading end of the core pin, thereby establishing a precise depth of the axial bore. In another preferred embodiment, the injection pressure circumferentially compresses the sleeve against the core pin, thereby co-axially centering the sleeve relative to the core pin, and thus an outer cylindrical surface of the resultant hub. With this one preferred embodiment, the compression of the sleeve is in the form of elastic deformation.